1. Field of the Invention
The present invention relates to a method of calibrating a surface texture measurement device. Specifically, the present invention relates to a method of calibrating a surface texture measurement device that measures the shape, roughness, and the like of a measured object by tracing the surface thereof with a stylus.
2. Description of Related Art
A surface texture measurement device is known that moves a stylus along a surface of a measured object in a state where the stylus is in contact with the surface of the measured object, detects a displacement of the stylus caused by the surface shape and surface roughness of the measured object, and measures the surface texture, such as the shape and roughness, of the measured object from the displacement of the stylus.
Such a surface texture measurement device normally has a detector including a measurement arm swingably supported at a rotation axis as a support point, a stylus provided in an end of the measurement arm, and a detection unit that detects a swing amount of the measurement arm; a stage holding a measured object; and a relative movement mechanism relatively moving the detector and the stage. For measurement, in a state where the stylus is in contact with the surface of the measured object, the relative movement mechanism relatively moves the detector and the stage and then the detector detects a swing amount of the measurement arm. The device measures the surface texture of the measured object based on the swing amount.
To measure the upper and lower surfaces of the internal diameter of a cylindrical workpiece using such a surface texture measurement device, for example, it is conventionally required to attach an arm having a downward stylus at the end to a detector main body, measure the lower surface of the internal diameter of the cylindrical workpiece, remove the arm, change the direction of the stylus to upward, attach the arm to the detector main body, and measure the upper surface of the internal diameter of the cylindrical workpiece. Measurement thus takes time due to removal and attachment of the aim.
A structure is proposed that allows measurement of the upper and lower surfaces of the internal diameter of a cylindrical workpiece without requiring removal and attachment of a measurement arm (Japanese Patent Laid-open Publication No. S58-83201). In the structure, an upward stylus and a downward stylus are provided to an end of the measurement arm. The end of the measurement arm is urged upward to allow the upward stylus to measure the upper surface of the internal diameter of the cylindrical workpiece. Then, the end of the measurement arm is switched to be urged downward to allow the downward stylus to measure the lower surface of the internal diameter of the cylindrical workpiece.
With the surface texture measurement device above having the upward stylus and the downward stylus, however, the mutual relationship cannot be accurately evaluated between the measurement results provided by the upward stylus and the measurement results provided by the downward stylus unless the mutual positional relationship of the upward stylus and the downward stylus is accurately known. To measure the thickness of a measured object, for instance, the shape of the lower surface of the measured object is measured with the upward stylus; the shape of the upper surface of the measured object is measured with the downward stylus; and the thickness of the measured object is then obtained from the measurement results of the lower surface and the measurement results of the upper surface. Unless the mutual positional relationship of the upward stylus and the downward stylus is accurately known, the thickness of the measured object cannot be accurately evaluated.